Synthesis of α,β-Epoxyacyl Azides and Their Rearrangement to Epoxy Isocyanates and 3- and 4-Oxazolin-2-ones

Article abstract of DOI:10.1021/jo00186a030

The conversion of α,β-epoxy carboxylates 6 into α,β-epoxyacyl azides 4 proceeds either via reaction of the mixed anhydrides 7 with sodium azide or via reaction of epoxyacyl chlorides 8 with hydrazoic acid-pyridine.The latter method is preferred.The azides 4 undergo a smooth thermal Curtius rearrangement to give 4-oxazolin-2-ones 10 for the substrates 4a-h having a hydrogen atom at C(β).Monitoring this reaction by means of IR shows that the epoxy isocyanates 5 are intermediates.Intramolecular ring expansion of 5 then leads to 3-oxazolin-2-ones 9 that tautomerizeto the 4-isomers 10a-h.Epoxyacyl azides 4i,n-q, having no hydrogen atom at C(β), producing 3-oxazolin-2-ones 9i,n-q by a proton shift is not possible.The products 9i and 9q rapidly add water at the imine bond to give oxazolidin-2-ones 11.Epoxy isocyanate 5k is reasonable stable in solution; reaction with methanol affords urethane 12.